Circuit breaker of gas blast type having insulator bushing means for externally locating an impedance means



1963 J. w. BEATTY CIRCUIT BREAKER 0F GAS BLAST TYPE HAVING INSULATOR BMEANS FOR EXTENALLY LOCATING AN IMPEDANCE MEANS Filed Sept. 22, 1960 6 l1 t 8 8 9 6 4m m Hw h. U t 3 W Inventor: John W. Beatbg, a/Jaw. W

Attorn e5.

Dec. 17, 1963 J. w. BEATTY ,8

CIRCUIT BREAKER OF GAS BLAST TYPE HAVING INSULATOR BUSHING MEANS FOREXTENALLY LOCATING AN IMPEDANCE MEANS Filed Sept. 22. 1960 2Sheets-Sheet 2 VJIIIIIIII Yl'llI/lll/i EM m m. T C e e B n mi nn M 1h-0. J u: b

United States Patent Clll CUlT BREAKER 0F GAS BLAiBT TYPE HAVINGINSULATUR BUEEHING MEAN FGR EXTER- NALLY LGCATHNG AN IMPEDANCE MEANSJohn W. Beatty, Newtown Equare, Pa, asslgnor to General Electric(Iornpany, a corporation of New York Filed Sept. 22, 1960, $92. No.57,747 9 Claims. (6i. 290 448) This invention relates to an electriccircuit breaker of the gas-blast type and more particularly relates to acircuit breaker of this type which has voltage-controlling impedancemeans connected in shunt with its main contacts.

For controlling the voltage developed across the main contacts of thecircuit breaker during a circuit-interrupting operation, it has beencustomary to shunt these contacts with an impedance through whichcurrent is transferred when the main contacts are separated to interruptthe circuit. For interrupting the current through the impedance, thereis customarily provided an auxiliary switch which opens within a fewcycles after the main contacts have been separated.

A typical gas-blast circuit breaker containing such avoltage-controlling impedance and auxiliary switch is shown and claimedin US. Patent 2,911,546 to Oppel, assigned to the assignee of thepresent inveniton. In the circuit breaker of that patent, thevoltage-controlling impedance is a resistor located within a tank thatsurrounds both the main contacts of the breaker and the contacts of theauxiliary switch. This tank is filled with pressurized gas that acts toextinguish the arcs drawn at the main contacts and the auxiliarycontacts during a circuit-interrupting operation.

Locating the resistor internally of the tank presents certain problems,particularly if the resistor is to be or" a relatively low ohmic value.One such problem is that a low ohmic resistor designed for the highcurrents involved is quite bulky and therefore difiicult to fit into thetank without necessitating certain design complications, such as aconsiderably larger tank than would otherwise be required. Anotherproblem is one of dissipating the large amounts of heat generated by therelatively high currents that will flow through a low ohmic resistorduring interruption. If the resistor is within the pressurized tank, thelarge amounts of heat generated will tend to raise the pressure andtemperature of the gas within the tank to unduly high levels.

One way of lessening these problems is to locate the resistor outside,rather than inside, the tank. Prior efforts along these lines have notbeen entirely successful, primarily due to the great expenses that havebeen involved in providing adequate insulation for the requiredconnections to the externally-located resistor. For example, one eifortalong these lines has required two auxiliary high voltage bushings, eachadequate to withstand substantially the same voltages as the mainterminal bushings of the breaker. Such auxiliary bushings are undulyexpensive.

Accordingly, an object of my invention is to construct the connectionbetween an externally located resistor and the usual power circuitthrough the breaker in such a manner that the connection requires anear-minimum of expensive insulation beyond that otherwise needed in thebreaker.

Another object is to construct the connection between the resistor andthe main power circuit through the breaker in such a manner that theadded insulation used for the connection is required to withstandconsiderably less voltage than the voltage that the main terminalbushings are required to withstand and is, moreover, required 3,114,816Patented Dec. 17, 1963 to withstand this lesser value of voltage onlyduring the short interval when current is flowing through the resister.

In carrying out my invention in one form, I provide a circuit breakercomprising a tank containing pressurized gas. A pair of separable maincontacts are located within the tank, and a main insulating bushingextends through a wall of the tank. The bushing comprises a tubular mainconductor electrically connected between one of the main contacts andterminal structure located at the outer end of the bushing. The bushingstructure also comprises a housing in which the tubular main conductoris supported. The housing comprises a hollow main insulator disposedexternally to the tank and surrounding a portion of the tubular mainconductor. Located externally to the tank and bushing isvoltage-controlling resistance means. Located internally of the tank arethe electrodes of an auxiliary switch. These auxiliary electrodes andthe resistor are connected in series with each other and in parallelwith the main contacts by conduc tive means comprising an auxiliaryconductor providing a connection between one terminal of the resistorand one of said auxiliary electrodes. This auxiliary conductor extendsthrough the bore of the tubular main conductor and is radially spacedtherefrom in electrically insulated relationship. A first auxiliaryinsulator of tubular form surrounds a portion of the auxiliary conductorand is disposed at the outer end of the main insulator for supportingone end of the auxiliary conductor. A second auxiliary insulator oftubular form surrounds another portion of the auxiliary conductor and isdisposed at the inner end of the bushing for supporting the other end ofthe auxiliary conductor.

For a better understanding of my invention reference may be had to thefollowing description taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a side elevational view partly in section showing a circuitbreaker embodying one form of my inven tion.

FIG. 2 is a cross-sectional view of a portion of the breaker shown inFIG. 1.

FIG. 3 is a diagrammatic view of the circuit breaker shown in itsfully-closed position.

FIG. 4 is a diagrammatic view of the circuit breaker of FIG. 1 shown inits fully-open position.

FIG. 5 is a diagrammatic view showing the circuit breaker of FIG. 1 in apartially-open position in which its main contacts are open but itsauxiliary contacts are still closed.

Referring now to FIG. 1, the circuit breaker shown therein is of thegeneral type shown and claimed in my Patent 2,783,338 and in Patent No.2,911,546 to Oppel, both of which are assigned to the assignee of thepresent invention. This circuit breaker comprises an enclosedinterrupting chamber defined, in part, by a metallic tank 10 which isfilled with pressurized arc extinguishing gas, preferably air.

Disposed within the tank 10 are two pairs 11 and 1 2 of separable maincontacts connected in series-circuit relationship. Each pair ofseparable main contacts comprises a stationary contact 13 or 14 and amovable contact 15 or 16. The movable contacts 15 and 16 are pivotallymounted on a central metallic housing 17 which is electrically connectedto the tank and which provides a conductive path interconnecting the twomovable contacts 15 and 16. The movable contacts 15 and 16 are adaptedto be simultaneously separated from their respective stationary contacts13 and 14 by means of an operating mechanism generally indicated at 18acting through a set of connecting links 19. The details of thisoperating mechanism form no part of the present invention and aretherefore not shown in the drawing. Pref- 9 erably, however, thismechanism is constructed as shown and claimed in my aforementionedpatent.

When the main contacts are separated by the operating mechanism 13, anarc is formed across each intercontact gap. This arc is quicklyextinguished by flow of pressurized gas from the tank 149 to theexterior of the tank via a path extending through the inter-contact gapand through a nozzle structure 21 formed in the central housing 17. Thepath of this gas how is indicated by the arrows 2b in FIG. 1. This flowof pressurized gas is controlled by suitable valve means (not shown)internally of the central housing 17 and such valve means interrupts theflow of pressurized gas as soon as the circuit is interrupted. A moredetailed description of the interrupting operation will appearhereinafter.

The main stationary contacts 13 and 14 are respectively supported on theinner ends of terminal bushings 25 and 26 extending through alignedopenings provided in the wall of tank It). These bushings each comprisecentrally-disposed conductive studs for carrying electric power to andfrom the contacts of the breaker through the openings in the wall of thetank It). The conductive stud of bushing 25 is a tubular metallic member2'7 connected through metallic adapter structure 3% to the stationarycontact 13. The adapter structure comprises a conductivecontact-mounting block 32 and an end plate 3 mechanically andelectrically connected together by means of circumferentially-spacedmetallic rods 35. Each of these metallic rods is Welded or otherwisesecured at its opposite ends to the parts 32 and 34, respectively. Atthe opposite, or outer, end of the stud 27, there is a conductive nut5t) that forms a terminal for the circuit breaker to which a power line36 is suitably connected. The stud 27 is thus electrically connectedbetween the terminal structure 5% and the contacts 11 of tie circuitbreaker.

When the main contacts of the circuit breaker are in open position, thetank lltl is at approximately a midpotential with respect to the twoconductive studs extending through the bushings 2S and 26. Under theseopen circuit conditions, the insulation of these bushings and 26 servesto electrically insulate their respective conductive studs from the tank1b, as will soon be described. Since the bushings 25 and 26 aresubstantially identical, only one will be described in detail.

Referring now to FIG. 2 which is a detailed cross-sectional view ofbushing 25, it can be seen that the bushing comprises a tubular housingiii, 41, 42 surrounding the tubular conductive stud 27. This tubularhousing is composed of a plurality of tubular insulating shells as and41, preferably of porcelain, and a metallic tubular support 42 disposedbetween the two shells 4d and ill. End plates 34 and 44 are disposed atopposite ends of the housing 4-0, 41, 42, and through these end platesare transmitted forces tending to compress the insulating shells and 41,as will soon be apparent. A portion of the total force acting throughthe end plates as and to compress the insulating shells 4d and 41 isderived from a spring assembly 46 of Belleville-type compression springsdisposed at the outer end of bushing 25. This compression springassembly bears at one end against the end plate 44 and at its oppositeend against force-transmitting structure mounted on the outer end ofstud 27. This force-transmitting structure comprises an annular thrustWasher 48 surounding an abutment in the form of a nut 50 threaded ontothe outer end of conductive stud 27. This nut 50 has a flange at itsouter end carrying a series of jack screws 52 that bear against theannular thrust washer 48. These jack screws 52 can be suitably adjustedto vary the compression of the spring assembly 46. Since the compressionspring assembly 46 is disposed between the end plate 44 and theforce-transmitting structure 48, 50 attached to the end of conductivestud 27, it Will be apparent that the spring assembly 46, in seeking toexpand, tends to force the end plate 34 to the right and the end plate44 to the left, thus compressing the two insulating shells til and 41between the end plates 34 and 44 and at the same time loading theconductive stud 27 in tension. The spring assembly 45 serves thedesirable purpose of maintaining the insulating shells in compressiondespite unequal expansion of the main conductor 27 and the housing 40,41, 42 of the bushing. The spring assembly 46 also serves to force theend plate into sealed relationship with the porcelain shell 41 and tomaintain this sealed relationship despite unequal expansion of the mainconductor 27 and the housing id, 41 4-2.

Between the housing 4-0, 41, 42 and the stud 27 there is a generallycylindrical chamber 55 that communicates with the pressurized gas in thetank 10 through openings 57 provided in the end plate 34. Thus, thechamber 5'5 contains pressurized gas at the same pressure as the gas intank 1h. The pressurized gas in chamber 55 acts against a piston 59suitably clamped to the outer end of stud 27 to urge the piston 53% tothe righ This force tends to apply additional compressive forces to theinner insulating shell it A tube 60 of insulating material surrounds thepiston 59 and a flange 62 formed on the tubular support 42 to define acylindrical outer wall for the chamber 55. Suitable seals 63 areprovided between the tube 60 and the parts 59 and 62 to preventpressurized air from leaking axially past the tube 69 into the spacesurrounding the tube se. The space between the tube at} and theporcelain shell 41 is preferably filled with an insulating gas, such assulfur hexailuoride, at a considerably lower pressure than the airwithin chamber 55.

Any suitable means may be used for holding the bushing 25 in placewithin its opening in wall tank 10, but I prefer to use the fasteningmeans shown and claimed in application SN. 843,589, Oppel, filedSeptember 30, 1959, now Patent No. 3,609,983, and assigned to theassignee of the present invention. This fastening means comprises aradially-split annular locking ring 7t? having an unstressed diameterslightly smaller than the diameter of a groove 72 provided in the outerperiphery of the tubular supporting member 42. This locking ring issnapped into the groove '72 and in this position bears against theinternal face of a reinforcing ring 73 Welded to the tank wall lltl. Thetubular supporting member 42 has a radially outwardly extending flangeexternal to the tank 110, and this flange carries jack screws 7 5threaded thereinto. When the jack screws are tightened, the reinforcingmembers '73 of the tank wall is clamped between the locking ring it? andthe jack screws '75.

For controlling the voltage developed across the contacts of a highvoltage circuit breaker, it is customary to provide resistance meansshunting the contacts of the breaker. The principal function of thisresistance means is to control the rate of rise and the peak value ofthe usual recovery voltage transient that appears across the opencontacts of the breaker following a current zero during thecircuit-interrupting operation.

In the disclosed circuit breaker, the resistor for performing thisfunction is schematically shown at disposed in a location outside thetank 10. This resistor 86 is preferably mounted on suitable conductivestructure e32 mechanically connected to the end plate 44 andelectrically connected to the terminal nut 5% through a suitableconductor 81. One terminal of the resistor 3% is electrically connectedto the conductive structure 81, 32 and the opposite terminal isconnected through a conductor S3 to the outer end of a conductive rod85. This conductive rod, also referred to hereinafter as an auxiliaryconductor extends in coaxial relationship through the tubular conductivestud 27 of the bushing into the tank It). This conductive rod isconnected at its inner end to one terminal 83 of an auxiliary, orresistor, switch 90 through a suitable conductor 9'7.

The auxiliary switch 9% comprises a pair of electrodes 91 and 92 spacedapart to form an interrupting gap therebetween. The electrode 91 issupported on the central housing 17 by means of an insulator 93 which iscapable of electrically isolating the electrode 91 from the centralhousing when the auxiliary switch is open. The electrode 92 is alsosupported on the central housing 17 but is electrically connected to thehousing. Electrically bridging the two stationary electrodes 91 and 92is a movable electrode 95 which in its closed position of FIG. 1 abutsagainst the two stationary electrodes. Thus, it will be seen that whenthe auxiliary switch 90 is closed, the series combination of theauxiliary switch 90 and the resistor 80 is connected in shunt with themain contacts 11 by means of a shunt circuit which extends through theparts 81, 82, 80, 83, 85, 87, 91, 95, 92 and 17.

The other set of main contacts 12 is shunted by a circuit similar to theshunt circuit described hereinabove around the main contacts 11. Sincethe parts forming this latter shunt circuit are substantially identicalto those forming the first shunt circuit, corresponding parts of thelatter circuit have been assigned corresponding reference numeralsfollowed by the suflix a.

The electrodes of the resistor or auxiliary switch may be thought of asbeing auxiliary contacts or electrodes for the overall circuit breakerand are frequently referred to in the present application as auxiliarycontacts or electrodes.

The auxiliary switches 91) and 9dr: are provided with a suitableoperating mechanism that is capable of opening the contacts of these twoswitches substantially simultaneously and within a short time after themain contacts part. This operating mechanism can be of any conventionalform but is preferably of the type shown and claimed in theaforementioned Oppel Patent 2,911,456. The details of the operatingmechanism form no part of the present invention and have not been shownin the drawing. For the purposes of the present invention, it issufficient to understand merely that the movable contacts 95 and 95a ofthe auxiliary switches 9i? and 9921 are con nected together by cross bar97 of insulating material, and this cross bar is coupled to the movablemain contacts 15 and 1 6 through an operating rod h 8. When the movablemaincontacts are driven into their open position, the operating rod 98and the cross bar 97 are driven upward and this lifts the movableauxiliary contacts 95 and 95:: from their respective stationaryelectrodes. The operating mechanism of the auxiliary switches is so constructed that the contacts of the auxiliary switches part at a preciselytimed interval (e.g., 1.2 cycles) after the main contacts part.

For insulating the main power circuit through the breaker from theconnection between the resistor 80 and the terminal 88 of the auxiliaryswitch 98, I provide a pair of cylindrical insulators 1% and 102 locatedat on posite ends of the terminal bushing 25. As will be apparent fromFIG. 2, each of these insulators surrounds the centrally disposedconductive rod 85 and provides a support for one end of the conductiverod. The outer insulator 100 is mounted on the outer end of the terminalbushing 25 and is clamped in compression between the nut 50 and anauxiliary end plate 164 by means including a nut 196 threaded on the endof conductive rod 85. A suitable compression spring assembly 108disposed'between the nut 106 and the end plate 104 controls the amountof clamping forces provided by the nut 113-6. The spring serves also tohold the insulator 106 in compression despite unequal expansions of thecentral rod 85 and the surrounding insulators and to maintain a sealedrelationship between the end plate 164 at the insulator m despite suchunequal expansions.

The other insulator 162 is clamped to the inner end of the bushing 25 byforces acting through an auxiliary end plate 110 bearing against theinner end of the insulator 19:2. This auxiliary end plate 116 is fixedto the conductive rod so that when the conductive rod 85 is forced tothe right by tightening of the nut 11% at the opposite end of theconductive rod 85, the end plate 116 is forced to the right intoclamping engagement with the auxiliary insulator 102. Thus, theinsulators lltltl and H92, are maintained in compression by forcesapplied to their ends through the conductive rod 35.

For providing insulation between the conductive rod and the mainconductor 27 of the bushin the bore of the tubular conductor 27 isradially spaced from the conductive rod 85 throughout the length of themain conductor 27 so as to provide an insulating space 112 between theconductive rod 85 and the main conductor 27.

insulating space 1 12 is filled with pressurized gas at the samepressure as the gas of the tank 1h since an opening 114- is provided inthe end plate to afiord communication between the gas in tank 1d and thein sulating space 1 12. Since this gas is at a relatively high pressure,only a small separation between the concentric parts 27 and 595 isneeded to withstand a relatively high voltage between these parts. Incertain applications, the space between the parts 217 and 85 can befilled with a solid or liquid insulating material instead of the gaseousinsulating material shown.

The high pressure gas within auxiliary insulator N2 subjects thisinsulator to no appreciable stresses since gas at the same pressure ispresent about the exterior of the auxiliary insulator 102. The otherauxiliary insulator Mill is protected from being stressed by the highpres sure gas therein by means of a tubular liner 12h of insulatingmaterial spaced from the bore of insulator 1%. This liner 1.243surrounds suitable flanges formed on the parts 50 and 164 respectively,and suitable seals provided between the flange and the liner prevent thepressurized gas from filling the space between the liner and thepercelain shell 1%. The clamping forces applied to the end plate 1%through the nut 1% hold the end plate in sealed relationship withrespect to the liner 12% against the gas pressure forces tending toforce the end plate 104 to the right.

When the circuit breaker is closed, there is no significant voltageapplied across the insulators 1% and 162 since the shunt circuitcomprising the resistor 89 and the then closed auxiliary switch 9b isshunted by the closed main contacts 11 of the breaker. This isillustrated in FIG. 3 which is a diagrammatic view of the circuitbreaker in closed circuit position.

When the circuit breaker is fully open, as depicted in the diagrammaticview of FIG. 4-, no current is flowing through the resistor fill sincethe auxiliary switch ht) is open. Thus, during this open circuitinterval, conductor 27 is at the same voltage as the conductivestructure 83, 85, 87 extending between the resistor as and the auxiliaryswitch 94 This being the case, no significant voltage would be presentacross the insulators ltlil or M2 or the gap 112, all of whichelectrically isolate the conductive structures 27 and 83, 85, $7.

The only time that voltage is present across the auxiliary insulatorsHill and 1&2 and the gap 112 is during the short interval (depicted inFIG. 5) when the main contacts 11 and 12 are open but the auxiliarycontacts have not yet been open. During this short interval, the voltageapplied between the main conductor 27 and the conductive structure 83,85, 87 is equal to the voltage drop across the resistor 8t). Even underthe most extreme transient conditions that could occur while the breakeris in its position of FIG. 5, e.g., those accompanying multiplelightning strokes, to the power line 36, the voltage drop across theresistor 80 is relatively small in comparison to the impulse voltageswhich the main insulators it) and 41 are required by industry standardsto withstand. In this latter connection, the most severe voltage burdenimposed on the main insulators 4t and 41 occurs when lightning strikesthe power line while both the main contacts 11 and the contacts ofauxiliary switch 9% are open. Under these particular conditions, thelightning surge upon reaching the line terminal of the open circuitbreaker has its crest value doubled through reflection at the circuitbreaker terminal. The resulting voltage peak, which will normally be themaximum encountered by the breaker, is applied across the maininsulators 4t and 41 but results in no appreciable voltage across theresistor St? since the auxiliary conductive structure $3, 35, 37 is atsubstantially the same voltage as the main conductor 27, as explained inconnection with FIG. 4. Thus, under the most severe voltage conditions,which are those which govern the design of the main insulators, noappreciable voltage is applied across the resistor till. it willtherefore be apparent that the insulators ltltl and 192, which arerequired to withstand only the voltage applied across the resistor 8t),may be designed for considerably lower impulse voltages than theinsulating shells 4i) and 41. For example, in a typical application ofmy invention, a circuit breaker having a main porcelain shell lltwenty-six inches in length may utilize an auxiliary porcelain insulator1% only about ten inches long.

While I have shown and described a particular embodiment of myinvention, it will be obvious to those skilled in the art that variouschanges and modifications may be made without departing from myinvention in its broader aspects, and I, therefore, intend in theappended claims to cover all such changes and modifications as fallwithin the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. An electric circuit breaker comprising a metal tank containingpressurized gas, a pair of separable main contacts located within saidtank, a main insulating bushing extending through a Wall of said tank,circuit breaker terminal structure mounted on the outer end of saidbushing, said bushing comprising a tubular main conductor electricallyconnected between one of said main contacts and said terminal structure,said bushing further comprising a housing including a hollow insulatordisposed exernally to said tank and surrounding a portion of saidtubular main conductor, means for supporting said conductor within saidhousing, resistance means located externally to said tank and saidbushing and having a pair of opposed terminals, an auxiliary switchcomprising auxiliary electrodes located within said tank, conductormeans for connecting said auxiliary electrodes and said resistance meansin series with each other and in parallel with said main contacts, saidconductor means comprising an auxiliary conductor providing a connectionbetween one terminal of said resistance means and one of said auxiliaryelectrodes, said auxiliary conductor extending through the bore of saidtubular main conductor and radially-spaced therefrom in electricallyinsulated relationship to the tubular main conductor, a first auxiliaryinsulator of tubular form surrounding a portion of said auxiliaryconductor and disposed at the outer end of said main insulator outwardlyof said circuit breaker terminal structure for supporting one end ofsaid auxiliary conductor, and a second auxiliary insulator of tubularform surrounding a portion of said auxiliary conductor and disposed atthe inner end of said bushing for supporting the other end of saidauxiliary conductor said conductor means comprising additionalconductive structure connected between said circuit breaker terminalstructure and the other terminal of said resistance means, saidresistance means being located outside said auxiliary insulators.

2. In the circuit breaker of claim 1, means affording communicationbetween the interior of said tank and the space between said tubularmain conductor and said auxiliary conductor so that pressurized gas fromsaid tank is present within said space.

3. The circuit breaker of claim 1 in which said second auxiliaryinsulator is disposed in the pressurized gas within said tank and inwhich means are provided to afford communication between the interior ofsaid tank and the interior of said second auxiliary insulator so thatsubstantially equal pressures are present internally and externally or"said second auxiliary insulator.

4. The circuit breaker of claim 1 in which said second auxiliaryinsulator is disposed in the pressurized gas within said tank, in whichmeans is provided to aiford communication between the interior of saidtank and the interior of said second auxiliary insulator, and in whichmeans is provided to afford communication between the interior of saidsecond auxiliary insulator and the space between said tubular mainconductor and the interior of said second auxiliary insulator so thatpressurized gas from the tank is present within said auxiliary insulatorand within said space.

S. The circuit breaker of claim 1 in which said auxiliary conductorcomprises a conductive rod extending between opposite ends of saidauxiliary insulators and in which there is provided means for loadingsaid auxiliary insulators in compression and said conductive rod intension comprising spring means disposed between one of said auxiliaryinsulators and said conductive rod.

6. An electric circuit breaker comprising a tank containing pressurizedgas, a pair of separable main contacts located within said tank, a maininsulating bushing extending through a wall of said tank, terminalstructure mounted on the outer end of said bushing, said bushingcomprising a tubular main conductor electrically connected between oneof said main contacts and said terminal structure, said bushing furthercomprising a housing including a hollow insulator disposed externally tosaid tank and another hollow insulator disposed internally to said tank,means for mounting said tubular main conductor within said housing withsaid hollow insulators surrounding said tubular main conductor, anabutment fixed to one end of said tubular main conductor, means forloading said insulators in compression and said tubular main conductorin tension comprising spring means between one of said insulators andsaid abutment, resistance means located externally to said tank and saidbushing, an auxiliary switch comprising auxiliary electrodes locatedwithin said tank, conductive means for connecting said auxiliaryelectrodes and said resistance means in series with each other and inparallel with said main contacts, said conductive means comprising anauxiliary conductor providing a connection between one terminal of saidresistor and one of said auxiliary electrodes, said auxiliary conductorextending through the bore of said tubular conductor and radially spacedtherefrom in electrically insulated relationship to the tubularconductor, a pair of auxiliary insulators of tubular form mounted atopposite ends of said bushing and surrounding said auxiliary conductorin radially-spaced relationship to said auxiliary conductor, and meanslocated at opposite ends of said auxiliary insulators for mounting saidauxiliary conductor on said auxiliary insulators.

7. An electric circuit breaker comprising a tank containing pressurizedgas, a pair of separable main contacts located within said tank, a maininsulating bushing extending through a wall of said tank, terminalstructure mounted on the outer end of said bushing, said bushingcomprising a tubular main conductor electrically connected between oneof said main contacts and said terminal structure, said bushing furthercomprising a housing including a hollow insulator disposed externally tosaid tank and another hollow insulator disposed internally to said tank,means for mounting said tubular main conductor within said housing withsaid hollow insulator surrounding said tubular main conductor, anabutment fixed to one end of said tubular main conductor, means forloading said insulators in compression and said tubular main conductorin tension comprising spring means between one of said insulators andsaid abutment, resistance means located externally to said tank and saidbushing, an auxiliary switch comprising auxiliary electrodes locatedwithin said tank, conductive means for connecting said auxiliaryelectrodes and said resistance means in series with each other and inparallel with said main contacts, said conductive means comprising anauxiliary conductor providing a connection between one terminal of saidresistor and one of said auxiliary electrodes, said auxiliary conductorextending through the bore of said tubular conductor and radially-spacedtherefrom in electrically-insulated relationship to the tubularconductor, a first auxiliary insulator of tubular form surrounding aportion of said auxiliary conductor disposed at the outer end of one ofsaid main insulators for supporting one end of said auxiliary conductor,means for mounting said auxiliary insulator in fixed relationship tosaid abutment, and a second auxiliary insulator of tubular formsurrounding a portion of said auxiliary conductor and disposed at theinner end of said bushing for sup porting the other end of saidauxiliary conductor.

8. The circuit breaker of claim 6 in which said auxiliary conductorcomprises a conductive rod extending between opposite ends of saidauxiliary insulators, and in which there is provided means for loadingsaid auxiliary insulators in compression and said conductive rod intension comprising spring means disposed between one of said auxiliaryinsulators and said conductive rod.

9. An electric circuit breaker comprising a metal tank, a pair ofseparable main contacts located within said tank, a main insulatingbushing extending through a wall of said tank, circuit breaker terminalstructure mounted on the outer end of said bushing, said bushingcomprising a tubular main conductor electrically connected between oneof said main contacts and said terminal structure, said bushing furthercomprising a housing including a hollow insulator disposed externally tosaid tank and surrounding a portion of said tubular main conductor,means for supporting said conductor within said housing, resistancemeans located externally to said tank and said bushing and having a pairof opposed terminals, an auxiliary switch comprising auxiliaryelectrodes 10- cated within said tank, conductor means for connectingsaid auxiliary electrodes and said resistance means in series with eachother and in parallel with said main contacts, said conductor meanscomprising an auxiliary conductor providing a connection between oneterminal of said resistance means and one of said auxiliary electrodes,said auxiliary conductor extending through the bore of said tubular mainconductor and radially-spaced therefrom in electrically insulatedrelationship to the tubular main conductor, a pair of auxiliaryinsulators of tubular form mounted at opposite ends of said bushing andsurrounding said auxiliary conductor in radially-spaced relationship,and means located at opposite ends of said auxiliary insulators formounting said auxiliary conductor on said auxiliary insulators saidconductor means further comprising conductive structure connectedbetween said circuit breaker terminal structure and the other terminalof said resistance means, and said resistance means being locatedoutside said auxiliary insulators.

References Cited in the file of this patent UNITED STATES PATENTS1,957,982 Smith May 8, 1934 1,969,911 Smith Aug. 4, 1934 2,349,095Henley May 16, 1944 2,729,721 Forwald Jan. 3, 1956 2,786,117 ForwaldMar. 19, 1957 2,866,173 Newcombe Dec. 23, 1958 2,911,546 Oppel Nov. 3,1959 2,921,168 Forwald Jan. 12, 1960 3,009,983 Oppel Nov. 21, 1961FOREIGN PATENTS 933,819 Germany Oct. 6, 1955 1,062,788 Germany H Aug. 6,1959 1,218,276 France Dec. 14, 1959

1. AN ELECTRIC CIRCUIT BREAKER COMPRISING A METAL TANK CONTAINING PRESSURIZED GAS, A PAIR OF SEPARABLE MAIN CONTACTS LOCATED WITHIN SAID TANK, A MAIN INSULATING BUSHING EXTENDING THROUGH A WALL OF SAID TANK, CIRCUIT BREAKER TERMINAL STRUCTURE MOUNTED ON THE OUTER END OF SAID BUSHING, SAID BUSHING COMPRISING A TUBULAR MAIN CONDUCTOR ELECTRICALLY CONNECTED BETWEEN ONE OF SAID MAIN CONTACTS AND SAID TERMINAL STRUCTURE, SAID BUSHING FURTHER COMPRISING A HOUSING INCLUDING A HOLLOW INSULATOR DISPOSED EXTERNALLY TO SAID TANK AND SURROUNDING A PORTION OF SAID TUBULAR MAIN CONDUCTOR, MEANS FOR SUPPORTING SAID CONDUCTOR WITHIN SAID HOUSING, RESISTANCE MEANS LOCATED EXTERNALLY TO SAID TANK AND SAID BUSHING AND HAVING A PAIR OF OPPOSED TERMINALS, AN AUXILIARY SWITCH COMPRISING AUXILIARY ELECTRODES LOCATED WITHIN SAID TANK, CONDUCTOR MEANS FOR CONNECTING SAID AUXILIARY ELECTRODES AND SAID RESISTANCE MEANS IN SERIES WITH EACH OTHER AND IN PARALLEL WITH SAID MAIN CONTACTS, SAID CONDUCTOR MEANS COMPRISING AN AUXILIARY CONDUCTOR PROVIDING A CONNECTION BETWEEN ONE TERMINAL OF SAID RESISTANCE MEANS AND ONE OF SAID AUXILIARY ELECTRODES, SAID AUXILIARY CONDUCTOR EXTENDING THROUGH THE BORE OF SAID TUBULAR MAIN CONDUCTOR AND RADIALLY-SPACED THEREFROM IN ELECTRICALLY INSULATED RELATIONSHIP TO THE TUBULAR MAIN CONDUCTOR, A FIRST AUXILIARY INSULATOR OF TUBULAR FORM SURROUNDING A PORTION OF SAID AUXILIARY CONDUCTOR AND DISPOSED AT THE OUTER END OF SAID MAIN INSULATOR OUTWARDLY OF SAID CIRCUIT BREAKER TERMINAL STRUCTURE FOR SUPPORTING ONE END OF SAID AUXILIARY CONDUCTOR, AND A SECOND AUXILIARY INSULATOR OF TUBULAR FORM SURROUNDING A PORTION OF SAID AUXILIARY CONDUCTOR AND DISPOSED AT THE INNER END OF SAID BUSHING FOR SUPPORTING THE OTHER END OF SAID AUXILIARY CONDUCTOR SAID CONDUCTOR MEANS COMPRISING ADDITIONAL CONDUCTIVE STRUCTURE CONNECTED BETWEEN SAID CIRCUIT BREAKER TERMINAL STRUCTURE AND THE OTHER TERMINAL OF SAID RESISTANCE MEANS, SAID RESISTANCE MEANS BEING LOCATED OUTSIDE SAID AUXILIARY INSULATORS. 